Top cross section measurements with CMS

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Top cross section

measurements with CMS

CPAN days - Segovia - 02/12/2015 M.S.Soares, CIEMAT

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Outline

• Introduction

• Inclusive tt cross sections at 13 TeV

• Differential tt cross sections at 13 TeV

• Conclusions and outlook

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Outline

• Introduction

• Inclusive tt cross sections at 13 TeV

• Differential tt cross sections at 13 TeV

• Conclusions and outlook Strong lead

ership of

Spanish groups

in

CMS Top

Quark

physics

program

(analys

is, MC produc

tion,

coordination)

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Introduction

Snapshot of LHC RunI top quark production measurements 7 & 8 TeV

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Introduction

__

_ _

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Introduction

__

_ _

Two leptons (l=e,μ,τ):

“dilepton"

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Introduction

__

_ _

Single lepton:

“l+jets”

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Introduction

__

_ _

Zero leptons:

“hadronic”

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Introduction

Inclusive tt production measured in almost all possible final states

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Introduction

Ultimate precision on inclusive tt cross section: 5% theory~experiment

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Introduction

Used to set limits on new physics

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Introduction

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Introduction

• Differential: interesting feature e.g. σ_tt function of top quark p_T

(GeV) Leading top pT

0 100 200 300 400 500

Data / (Madgraph + Pythia6)

0.4 0.6 0.8 1 1.2 1.4

1.6 Parton level

lepton+jets dilepton all-jets linear fit

8 TeV

CMS

+1.14 100 GeV

pT

r = -0.102⋅

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Introduction

• Differential: interesting feature e.g. σ_tt function of top quark p_T

• Meanwhile, on the theoretical side of the world...

(GeV) Leading top pT

0 100 200 300 400 500

Data / (Madgraph + Pythia6)

0.4 0.6 0.8 1 1.2 1.4

1.6 Parton level

lepton+jets dilepton all-jets linear fit

8 TeV

CMS

+1.14 100 GeV

pT

r = -0.102⋅

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NNLO calculation!

•Brand new calculations, Nov/15

(M.Czakon, D.Heymes, A.Mitov, arXiv:1511.00549)

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NNLO calculation!

•Brand new calculations, ^Nov/15

•Seems to be an indication of missing higher order

corrections

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NNLO calculation!

•Brand new calculations, Nov/15

•Seems to be an indication of missing higher order

corrections

•Crucial: early check of this behaviour at new energy!

•More: will a striking sign of new physics show up at 13 TeV?

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This talk: run II

Very first pp collisions at 13 TeV Integrated luminosity: 42 - 71pb^-1

Bunch spacing:

50 ns 25 ns

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This talk: run II

Very first pp collisions at 13 TeV Integrated luminosity: 42 - 71pb^-1

Bunch spacing:

50 ns 25 ns

samples of ~1000 to 2000 events after

selection efficiency

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Inclusive measurements

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• One electron and one muon

• p_T>20 GeV, isolated

• At least 2 jets

• p_T>30 GeV

• (no b-tag requirement)

New w.r.t. 8 TeV: new generation of NLO MC: POWHEG+Pythia8 great improvement on tt modelling - dominant syst uncertainty

• Exactly one electron or one muon

• At least 4 jets

• p_T>30 GeV

• 1 identified as coming from b-quark

Dilepton: Single-lepton:

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• Simple “cut-and-count” analyses

• Efficiencies (trigger, jets, b-jets and leptons detection) estimated in data/MC

• (low stat data: larger systematic uncertainties!)

• Dilepton (small backgrounds)

• DY and misidentified leptons from control regions in data

• tW, VV (V=vector boson) from MC

• Single-lepton (larger backgrounds reduced with btag requirement)

• QCD from control regions in data

• W+jets, single-top, DY from MC

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Dilepton events: eμ channel

TOP-15-003

to appear soon in PRL

sensitive to new physics

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TOP-15-003

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TOP-15-003

σtt=769±60(stat)±55(syst)

±92(lumi) pb

NNLO+NNLL: 832+40-46 pb

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e+jets and μ+jets final states

σ_tt=836±27(stat)±84(syst)

±100(lumi) pb

TOP-15-005

NNLO+NNLL: 832+40-46 pb

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[TeV]

s

2 4 6 8 10 12 14

cross section [pb]tInclusive t

10 102

103 CMS Preliminary

* Preliminary

-1) 8.8 fb Tevatron combined* 1.96 TeV (L ≤

-1)

* 7 TeV (L = 5 fb CMS eµ

-1) CMS l+jets 7 TeV (L = 2.3 fb

-1)

* 8 TeV (L = 19.7 fb CMS eµ

-1) CMS l+jets* 8 TeV (L = 2.8 fb

-1)

* 8 TeV (L = 5.3-20.3 fb LHC combined eµ

-1) 13 TeV (L = 42 pb CMS eµ

-1) CMS l+jets* 13 TeV (L = 42 pb

NNLO+NNLL (pp) ) p NNLO+NNLL (p

Czakon, Fiedler, Mitov, PRL 110 (2013) 252004

uncertainties according to PDF4LHC αS

= 172.5 GeV, PDF ⊕ mtop

[TeV]

13 s

600 800 1000

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Differential measurements

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• One pair: eμ, ee, μμ

• p_T>20 GeV, isolated

• At least 2 jets

• p_T>30 GeV

• 1 b-tag

Profited from same estimations of efficiencies, MC corrections, bkg estimations from inclusive measurements (differences highlighted)

• Exactly one electron or one muon

• At least 4 jets

• p_T>30 GeV

• 1 or 2 b-tags

Dilepton: Single-lepton:

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• Counting of event in bins, as function of

• tt system variables - reconstructed using Kinematic Fitter

• general event variables - no tt reconstruction

• Most of the corrections (+bkg estimation) identical to inclusive measurement

• Distributions unfolded taking into account correlations

• Results compared to MC predictions

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TOP-15-010 TOP-15-005

l+jets dilepton

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TOP-15-010 TOP-15-005

l+jets dilepton

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TOP-15-010 TOP-15-005

dilepton l+jets

Top pT spetrend as 8 ctra: similaTeV r

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TOP-15-010 TOP-15-005

Validation of new MC at 13 TeV

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TOP-15-010 TOP-15-005

Many other distributions

(not shown)

available in CMS PASes

and public twiki

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l+jets (event variables)

TOP-15-013

larger dataset: 71 fb^-1

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TOP-15-013

Detailed look at tt events

•unfold to “particle level”, visible space (reduce model dependency, but comparison with theory affected by

selection)

•check general aspects of event activity (important if dataset used to

search for new physics)

•variables:

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Detailed look at tt events

•unfold to “particle level”, visible space (reduce model dependency, but comparison with theory affected by

selection)

•check general aspects of event activity (important if dataset used to

search for new physics)

•variables:

TOP-15-013

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TOP-15-013

39

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TOP-15-013

40

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TOP-15-013

41

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TOP-15-013

42

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TOP-15-013

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Activity in tt events:

as expected No anomalies Good data-MC

agreement

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Conclusions and Outlook

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Conclusions

Measurements in this talk used 42 (71) pb^-1 of luminosity

Bunch spacing:

50 ns 25 ns

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Conclusions

• Very first set of pp collisions data at 13 TeV were used to investigate top pair production at the LHC

• Detector commissioned at this new energy, data fairly well understood

• Inclusive measurements agree with the standard model predictions at NNLO

• Differential cross sections as functions of top quark kinematic variables (within

uncertainties) show similar trend as observed at 8 TeV ➨ side by side with theorists

• Differential cross sections as functions of event variables indicate no deviation from the SM predictions

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Outlook

Measurements in this talk used 42 (71) pb^-1 of luminosity More than 2fb^-1 of “good data” available

Bunch spacing:

50 ns 25 ns

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Outlook

•2015 pp run ended in November (somewhat less luminosity than foreseen)

•Substantially more data than used for the Early Analyses

•statistic limitations also affect systematic uncertainties: new efficiencies, corrections, ‘working points’ defining objects to quickly improve Early Analysis precision (beyond statistics)

•Ingenuity at work:

•more sophisticated methods can be used to extract information from data

•details on differential distributions, e.g. top p_T spectra, coming to be fully understood

•top quark cross sections may be used to search for new physics

•CMS, with strong Spanish participation, active on a rich program involving top quark production

•will nature be so kind to show us signs of new physics within this program?